Thermocouple tube



Feb. 27, 1951 A. J. KLING THERMOCOUPLE TUBE Filed Nov. 29, 1939 PLATINUM3L AC/f Patented Feb. 27, 1951 UNITED STATES THERMOCOUPLE TUBEApplication November 29, 1939, Serial No. 306,750

' 1 Claim. 1

This invention generically relates to thermoresponsive devices adaptedto be used with the apparatus described and claimed in the applicationof Charles F. Green, filed November 29, 1939, Serial N0. 306,753, andthat of Laurens A. Taylor, filed November 29, 1939, Serial No. 366,755,more especially it is directed to a thermo-couple tube evacuated to ahigh degree and provided with a window having a high transmissioncoefficient for low temperature radiation.

One object of this invention is to provide a thermo-couple tubeevacuated to a high degree and including a rock salt window and a glassenvelope or bulb, the window and bulb being interconnected so that thestrains produced by the difference in expansion between the rock saltwindow and the glass bulb will be absorbed for the purpose of preventingcracking of the window.

Another object of this invention is to provide a highly evacuatedthermo-couple tube embodying a glass envelope-or bulb and a rock saltwindow, the rock salt window being connected to the glass bulb so as toprevent cracking of the window during or after the tube has beensubjected to the high temperatures incidental to the creation of thevacuum.

Another object of this invention is to provide a highly evacuatedtherrno-couple tube adapted to contain thermo electric generating unitsand embodying an optical rock salt window and a lead glass envelope orbulb, the rock salt window and glass bulb being connected by means of asilver sleeve adapted to absorb the strains produced by the unequalexpansion thereof, as a result of the high temperatures incidental tothe creation of a high degree of'vacuum. 7

Another object of this invention is to provide a highly evacuatedthermo-couple tube embodying an optical rock salt window and a leadglass bulb, the. window and bulb being united through theinstrumentality of a strain absorbing sleeve, the connection of saidsleeve with the rock salt window including a sealing means adapted tomaintain a high degree of vacuum over an indefinite period "and thetreatment of the inner and outer surfaces of the rock salt window beingsuch as to prevent the vapor from the rock salt causing a slowdeterioration of the tube.

With these and other objects in view, this invention consists in certainnovel details of construction, combination and arrangement of parts tobe more fully hereinafter described and claimed.

Referr ng more particularly to the accompanying drawings, in whichcorresponding parts are indicated by similar reference characters:

Fig. 1 is a perspective view of the thermo-couple tube constituting thesubject matter of this application and illustrating the mounting for thetube;

Fig. 2 is a sectionized perspective of the therrno-couple tube andillustrating the thermo-electric generating units within the tube andthe rods connecting the units and extending to the exterior of the tube;

Fig. 3 is a fragmentary longitudinal section of the thermo-couple tube,illustrating the manner of connecting the rock salt window to the leadglass envelope or bulb.

To solve the problem of a suitable window ma terial for thermo-coupletubes, transmission data was obtained on various types of glasses, mica,quartz, rock salt, fluorite, silver chloride and etc. The glasses ingeneral were highly opaque to low temperature radiation lying in theregion of that available from airplanes. Cf the glasses, lead glass hadthe most favorable coefiicient and it was found that very thin sectionsgave relatively good results, but these thicknesses were entirely toothin to be used in practical application to thermo-couple tubes. Quartzin crystal and fused form had low coefficients while sodium chloride(rock salt), potassium chloride, and calcium fluoride (fluorite) hadrelatively high coeflicients in thickness which could be used. Sodiumchloride was the best due to its transmission of the infrared radiationthrough a wider range of the spectrum than the other substances. Certainmanufactured silver chloride crystals gave high transmission, but thesecould not be reproduced later. These investigations resulted in theadoption of optical rock salt for window material. The use of rock salt,however, presented some exceedingly difiicult problems, among whichmight be mentioned connecting the rock salt window mater al to the glassbulb so that the window material would not crack when the tube wasexposed to the high temperatures incidental to evacuation; sealing therock salt window so as to maintain the high vacuum over an indefiniteperiod; providing a suitable seal ng material having a high coefficientfor low temperature radiation and preventing vapor from the windowmaterial causing slow deterioration of the tube. After many experiments,the tube forming the subject matter of the instant application wasfinally developed and this tube which is an improvement of thatdisclosed in my Patent No. 2,125,133, entitled Evacuated Receptacle,issued July 26, 1938, briefly stated, consists of a lead glass bulb 4,an optical rock salt window 1 connected to the bulb by means of a silversleeve 8, the latter having one end fused to the glass bulb and theother end sealed to the rock salt window, the inner and outer surfacesof the window being treated with a suitable asphaltum varnish I3.

In the illustrated embodiment characterizing this invention A is amounting for the thermocouple tube B. This mounting consists of acylindrical portion i into which the tube B is adapted to be inserted, apedestal 2 adapted to seat in a suitable support (not shown) and 3 aterminal panel carrying suitable terminal plates for the conductorsextending to the exterior of the tube.

Thermo-couple tube 13 which is positioned in cylinder portion l of themounting, as shown in Fig. 1, consists of a lead glass envelope or bulb4 which is sealed at its outer end by the stem or press 5 and open atits inner end as at 6. An optical rock salt window 7 is connected to theedge of opening 5 by means of a cylindrical metallic sleeve 9 preferablyof silver, although other metals having the requisite strain-absorbingpowers may be used. Silver sleeve 8 is tapered from its central portion9 to its opposite ends it! and H, as clearly shown in Fig. 3 of thedrawings.

The edge of bulb surrounding its open end 6 is fused over the end it ofsilver sleeve 8.

In order to seal the free end ll of sleeve 8 to the rock salt window l,the inner surface of the latter adjacent its periphery is formed with anannular groove 12, V-shaped in cross-section, as clearly shown in Fig. 3of the drawings. Annular groove I2 is adapted to be filled with aninorganic salt, in the present instance, silver chloride, the salt atthe time of its insertion in the groove being in a plastic state. Silverchloride was selected as a seal because of its high transmissioncoefiicient for low temperature radiation. When groove 52 has beenproperly filled with the silver chloride, the edge ii of sleeve 8 isforced through the material and into groove l2 until it reaches theposition shown in Fig. 3.

After the silver chloride has hardened the edge H of the silver sleeve 8will be effectively sealed in the groove 92 so as to maintain a highdegree of vacuum over an indefinite period.

- By connecting the rock salt window 1 to the glass bulb 6 through theinstrumentality of sleeve 8, the strains resulting from the differencein expansion of the glass and the rock salt window will be absorbed bythe sleeve and thus cracking of the window will be prevented when thetube is exposed to the high temperatures incidental to evacuation. Asthe evacuation temperatures also cause the rock salt window to give offcertain vapors, and to prevent these vapors causing tube deterioration,the inner and outer surfaces of the window are coated as at l3 with asuitable varnish such as asphaltum or the like.

- Within the tube B are mounted thermo-electrics units a and b which inthe present instance are in the form of thermo-couple strips l5|6arranged end to end and connected in bucking relation. Each of thestrips lE-lfi is composed of electrically dissimilar metals I! and I8united along junction line is, as clearly shown in Fig. 2 of thedrawings. lhe outer elements 11 of the respective strips are connectedto vertically disposed bars 20-4 I, while the inner elements there ofare bent backward and connected to the vertically disposed bar 22, asclearly shown in Fig. 2 of the drawings. Bars 20-2l are connected to andsupported by rods 23-24 while bar 22 is connected to and supported byrod 25. These rods extend through the tube and to the terminal plates(not shown) on panel 3 of mounting a, as will be understood withoutfurther discussion. Although in the present instance thermo-couples aand b are of the type described and claimed in the application ofLaurens A. Taylor, filed .November 29, 1939, Serial No. 306,755, it isto be understood that if desirable other units may be employed such asthose described in the copending applications of Charles F. Green, filedNovember 29, 1939 and serially numbered 306,753 and 306,754,respectively.

In conclusion, it will be seen this invention provides a thermo-coupletube having a rock salt window which will not crack when the tube hasbeen exposed to the high temperatures incidental to the creation of ahigh'vacuum; which will maintain the vacuum over an indefinite periodand which because of its high degree of vacuum characteristics willprovide an extremely sensitive thermo-couple tube.

Having described my invention, what I claim as new and wish to secure byLetters Patent is:

A thermo-couple tube comprising a lead glass envelope open at one endand sealed at the other, a rock salt window for the tube, coating meanson the inner and outer surfaces of the window to prevent slow tubedeterioration, said coating means being substantially coextensive withthe inner surface and coextensive with the outer surface on said window,a silver sleeve connecting the rock salt window and the edge surroundingthe open edge of said envelope, said edge being fused over the inner endof the sleeve, means for sealing the free end of the sleeve to the rocksalt window, said means including an inorganic salt having a hightransmission coefficient for low temperature radiation, means inconnection with the peripheral edge of said window to effect a reductionin radiation losses, said means including a coating of platinum blackapplied to said peripheral edge, and thermo-electric generating meanswithin the tube.

- I AUGUST J. KLING.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS OTHER REFERENCES A. I. E. 12., StandardDefinitions of Electrica Terms (1942), page 231.

